With climate change comes more pollen -- and a meaner allergy season

Associated PressPollen coats the leaves of a Japanese maple. With climate change, allergy seasons look to be longer and meaner. If you want to track the Northwest's changing climate, follow your nose. Early or extended periods of sneezing and wheezing could be signs our world is warming.

The environment has a huge impact on human health, influencing everything from the home territory of animals that spread disease to sunburns and skin cancer. And our environment is changing, with notable increases in global sea levels, average temperatures and levels of carbon dioxide in the atmosphere.

Scientists say these changes have already influenced human health, contributing to deadly heat waves in Europe and the Midwest, masses of jellyfish off Japan's coast and the spread of disease-carrying mosquitoes into more U.S. territory. As a warmer and more polluted world worsens allergies and asthma, one of climate change's biggest expected health impacts is breathing.

Many doctors think climate change helps explain why the amount of U.S. residents with asthma has roughly doubled since 1980, to more than 7 percent of adults and 9 percent of kids. That increase is a big worry, since asthma attacks hospitalize about half a million Americans each year, killing several thousand. Evidence also suggests that climate change is worsening allergies to certain pollen-bearing trees and weeds, but no one knows exactly how much.

The increase in carbon dioxide in the atmosphere, much of it from auto exhaust and other human activities, is one big contributor to climate change. Plants use CO2 to grow as people use oxygen. An increase in that gas, and the warming global temperatures it helps fuel, may cause a profusion of pollen among some plants in some places.

In Europe, scientists have found that higher temperatures cause earlier pollination in birch trees, a big springtime allergen. Scientists in northwest Italy noted that pollen seasons for several trees and weeds have started sooner and lasted longer since the 1980s.

American researchers have found that warmer temperatures and more carbon dioxide can make ragweed grow sooner and more robustly, putting out more of its allergenic pollen. The U.S. National Research Council issued a report last week which cited "limited evidence" that stinging nettles and poison ivy also grow better and become more toxic at higher temperatures and levels of carbon dioxide.

"There are a number of studies indicating that pollen season for trees and ragweed are likely to begin earlier with warming winters and longer growing seasons," said Lewis Ziska, a U.S. Department of Agriculture climate change expert.

Ziska said he doesn't have specific estimates for the Northwest. But conditions could be ripe here for more pollen. Scientists estimate the average temperature in the Northwest rose between 1 and 3 degrees during the 20th century and project a further increase of almost 3 degrees by 2030.

With ragweed growing in at least 10 Oregon counties and plenty of trees to spew pollen, rougher allergy seasons are predicted here. In 2004, 50 experts who met to discuss the impact of climate change on the Northwest agreed that a "longer and more intense allergy season" is "highly likely" in the coming decades.

The biggest worry for many allergy sufferers in Oregon is grass. The Willamette Valley is a major center of grass seed farming and, because of that, records some of the world's highest levels of grass pollen.

There's less research on how climate change specifically will affect grass, though Ziska said he hopes to study that. Academic and farming experts said that climate change hasn't had much impact on Oregon's grass crops so far. Temperature and sunlight both play a role in when the state's "cool season" grass crops start growing, said William Young, an Oregon State Extension specialist in seed production. But he said any changes have been "insignificant" compared to what would have to happen to hamper the grass industry dramatically.

Montanaro said some Oregon allergists have "seen a gradual increase in the grass season." The grass allergy season used to end around July 4 and now regularly runs through mid-July, he said. It's not clear how much of that change is due to climate or other factors, such as a move toward growing later-seeding grass crops.

Even if grass allergies don't get notably worse, there is plenty of reason to think climate change will make it harder for some to breathe. Increased plant and pollen production could not only worsen allergies but also asthma. More than half of adult asthma and 80 percent of childhood asthma has allergic triggers, Montanaro said. Scientists also expect climate change to increase the level of air pollutants that can trigger asthma attacks, including low-level ozone and tiny particles released by forest fires, which may get more common as the climate changes. It's impossible to predict just how much the climate will evolve and affect disease in coming decades, but the trends are worrisome.